It is a pop field using molecular character of absorption spectrum in infrared and tunable diode laser absorption spectroscopy to study many atmospheric trace gases absorption spectrum. Most of the molecular characteristic absorption is very weak, and the absorption line width is very narrow that can't be measured by traditional methods. Laser has become the perfect light source using in the atmosphere monitoring due to its monochromatic, directional and high power. The key technique of the tunable diode laser absorption spectroscopy (TDLAS) is the diode laser's character of high resolution and ability of tunable, it can even obtain the concentration of trace gas by measuring a single absorption line without interferes from others. A sensitive and precise atmosphere greenhouse gas continuous monitor is developed by combining the TDLAS with multi-pass cell and weak signal detect technique. The detect limit is lower than 0.087 mg/m3, and it can up to 17.5 mg/m3, that is enough for the ambient methane detection (1.16 mg/m3 in the air).